Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a multiple view liquid crystal display device that is capable of displaying a plurality of images in respective different directions, and the like.
Description of the Background Art
Liquid crystal display devices are used as the monitors of personal computers (PCs) and portable information terminal devices, or the display devices of TVs and the like, by utilizing advantages such as low power consumption, and small size and light weight. The liquid crystal display device is a device that includes a plurality of pixels that are arranged in a matrix, and optically modulates each of the pixels to display an image.
As the liquid crystal display device, an active matrix type liquid crystal display device that includes thin film transistors (TFTs) arranged in a matrix as switching elements is widely used.
Recently, there is developed a multiple view liquid crystal display device (plural screen liquid crystal display device) that is capable of displaying a plurality of images at different directional viewing angle by using a single liquid crystal display panel (liquid crystal panel). For example, Japanese Translation of PCT Application No. 2008-527440, Japanese Patent Application Laid-Open Nos. 2007-264082 and 2008-064917 each disclose a parallax barrier system multiple view liquid crystal display device, particularly, a double screen liquid crystal display device that displays different images (an image for right and an image for left) as viewed from right and left with respect to the front of the screen. Additionally, PCT International Publication No. WO2007/001071 discloses a vehicular double screen liquid crystal display device.
The parallax barrier system multiple view liquid crystal display device includes a liquid crystal panel, in which a plurality of types of pixels that display a plurality of images are mixed and arranged in accordance with a predetermined rule, and a light shielding layer called a parallax barrier, which is disposed on the front surface side (viewing side, display surface side) of the liquid crystal panel. The parallax barrier is arranged so as to shield light traveling in a specified direction from each pixel of the liquid crystal panel. Consequently, the light from the liquid crystal panel is separated in a plurality of directions, and the plurality of images displayed by the liquid crystal panel are displayed in respective different directions.
In the parallax barrier system multiple view liquid crystal display device has a problem of “crosstalk” that, into a first type image displayed in a certain direction, a part of a second type image that is different from the first type image and displayed in other direction is leaked, and is observed.
For example, in a case where crosstalk occurs in a parallax barrier system double screen liquid crystal display device that displays by dividing two images right and left, an image (image for left) to be displayed when a screen is viewed from the left with respect to the front, and an image (image for right) to be displayed when the screen is viewed from the right are viewed so as to overlap. This crosstalk occurs when the ranges of the viewing angles of the respective images overlap, and therefore is likely to occur in the vicinity of a boundary between viewing angle ranges of the plurality of images. That is, in the double screen liquid crystal display device, the crosstalk is likely to occur when the screen is viewed from the front of the screen, which is a boundary between a viewing angle range of the image for right and a viewing angle range of the image for left. Particularly, when an image that includes a lot of black display is displayed, even slight leak from other image causes easy visual recognition, and therefore an influence on an image quality is increased.
Generally, the liquid crystal panel includes a first substrate, on which pixel electrodes, switching elements that supply image signals to the pixel electrodes, signal lines, and the like are disposed, a second substrate, on which a black matrix that defines respective areas of pixels (pixel display areas), and a color filter (CF) are disposed, and liquid crystals that are sandwiched between these substrates. In the parallax barrier system double screen liquid crystal display device, a black matrix that defines a display pixel area is formed on a surface, opposed to a first substrate, of a second substrate, and a parallax barrier is formed on a surface opposite to the surface (viewing side). Accordingly, a gap corresponding to the thickness of the second substrate exists between the parallax barrier and the black matrix. The size of this gap is a factor for determining the direction and the width of the viewing angle range of each of the plurality of images that are displayed at the same time, along with the size of openings of the parallax barrier and the pitch of the pixels.
In the parallax barrier system multiple view liquid crystal display device, a phenomenon called “reverse viewing” that an image to be displayed in a reversed direction is viewed when the screen is viewed from a direction greatly deviated from the front is caused due to the gap between the parallax barrier and the black matrix. For example, when an observer moves to the right from the front of the screen with respect to the double screen liquid crystal display device, the image for right is first viewed. However, when the observer further continues to move to the right, a range in which the image for left is viewed appears. This is because other pixels adjacent to pixels to be originally viewed are viewed through the opening of the parallax barrier.
That is, in the parallax barrier system double screen liquid crystal display device, the viewing angle range of the image for left due to the reverse viewing phenomenon exists outside the viewing angle range of the image for right, and the viewing angle range of the image for right due to the reverse viewing phenomenon exists outside the viewing angle range of the image for left. Therefore, the crosstalk of the image for right and the image for left is likely to occur not only in the vicinity of the front of the screen, but also in the vicinity of the outer end (maximum viewing angle) of the viewing angle range of each of the image for right and the image for left, actually. Hereinafter, the crosstalk that occurs in the vicinity of the front of a screen is referred to as “front crosstalk”, and crosstalk resulting from the reverse viewing phenomenon that occurs in the vicinity of the outer end (maximum viewing angle) of the viewing angle range of each of images is referred to as “reverse viewing crosstalk”.
The front crosstalk and the reverse viewing crosstalk become problems also in not only the double screen liquid crystal display device, but also an arbitrary parallax barrier system multiple view liquid crystal display device.
A rate of crosstalk (intensity) that occurs in the multiple view liquid crystal display device can be expressed by the following Formula (1).Crosstalk rate=(WBB−BBB)/(min{WBB,BBB)  (1)
In Formula (1), WBB means (black luminance in white-black display), and BBB means (black luminance in black-black display).
That is, in Formula (1), WBB and BBB mean as follows:
WBB . . . Black luminance in white-black display: Luminance in a case where the observation side is black display and the other side is white display (black luminance)
BBB . . . Black luminance in black-black display: Luminance in a case where the observation side is black display and the other side is also black display (black luminance)
Formula (1) defines a rate of light that leaks from the other side where white display is performed relative to a visual field on one side where black display is performed. Form Formula (1), in order to reduce a crosstalk rate, two kinds of methods, that is, a method of decreasing the WBB (black luminance in white-black display), and a method of increasing the BBB (black luminance in black-black display) are effective. Decreasing the WBB (black luminance in white-black display) suppresses leak of light from the white display side, and means reduction of crosstalk itself.
Increasing the BBB (black luminance in black-black display), which is another method, means reduction in visibility of crosstalk. In Japanese Translation of PCT Application No. 2008-527440 discloses that the visibility of crosstalk is reduced by adding a certain intensity (luminance) to an individual image. When an image on the observer's side is black, the visibility of crosstalk becomes higher because of high sensitivity of human vision. The addition of a certain low level intensity makes the image move in a gray level range, in which the vision of a human is unlikely to react, thereby enabling the crosstalk to make inconspicuous. However, since the certain intensity is added to the individual image in black display, there is a problem that reduction in a contrast ratio is caused in all of the viewing angle ranges as an adverse effect.
The aforementioned Japanese Patent Application Laid-Open Nos. 2007-264082 and 2008-064917, and PCT International Publication No. WO2007/001071 each mainly disclose a method of mainly preventing front crosstalk of a double screen liquid crystal display device. However, a measure against reverse viewing crosstalk is not sufficient. For example, Japanese Patent Application Laid-Open No. 2007-264082 does not mention a problem of the reverse viewing crosstalk at all. Japanese Patent Application Laid-Open No. 2008-064917 suggests occurrence of the reverse viewing crosstalk, but does not take a particular effective measure. PCT International Publication No. WO2007/001071 indicates that a range, in which a reverse viewing phenomenon occurs, is a range mostly invisible from a driver's seat and a passenger seat (outside 45° or more from the front) in the vehicular double screen liquid crystal display device, but does not mention a method for practically preventing the reverse viewing crosstalk.